A biomechanical study of fast throwing movements of the shoulder in baseball pitching.

OBJECTIVE

To define the biomechanic function of the shoulder in fast throwing movements in baseball pitching.

METHODS

Using NAC high-speed video and PIAS LA-555 computer system, overhand pitching movements carried out by 12 healthy Japanese professional baseball pitchers were analyzed in three dimensions. The pitching motion was displayed as stick to sick figures dynamically.

RESULTS

Pitching motion was a combination of translational and rotational movements. Acceleration and deceleration, being two typical motion patterns, worked sequentially through the anatomic link system from the pivot leg to the pitching hand. During the acceleration phase, the shoulder joint acted as a junction point and a fulcrum, supporting the rotational acceleration motion, shoulder forward flexion and elbow extension. According to the changing glenohumeral angles of the pitching shoulder, shearing force turned into tension force which worked on the anterior shoulder structures and then shifted to the posterior part of the joint.

CONCLUSIONS

In fast throwing motion, the shoulder functions as an important fulcrum to support the pitching arm during the acceleration phase. Avoiding excessive stress and shearing force on the joint components and enhancing coordination of muscle action are important to a successful throwing motion and the prevention of shoulder injury.